Variable printer intensity control

ABSTRACT

Apparatus for printing characters with an impact intensity varying according to the surface area of the character being printed. Included in the apparatus is a cyclically movable character bearing member, such as a rotary print wheel or drum or an endless belt and one or more print hammers cooperable with the member forming a printing couple for printing characters. An electromagnetic field produced by a solenoid initiates the flight of the hammer against a document which may be moved relatively thereto as the printing operation is performed. The current through the solenoid coil is limited by resisters of different values which are controlled by electrical gates for selectively varying the amount of current supplied to the coil for driving the hammer. The timing of the printing is kept in synchronization with the document movement by means of an electromechanical clock capable of dividing each character position into an equal number of zones. During the operation of the printing apparatus, the sequence of accessing the digits to be printed, positioning the print wheel, and firing the hammer continues as the document moves through the apparatus. Associated with the print wheel and jointly rotatable therewith is a disk having a plurality of coded positions represented by apertures therein each position representing a printing character position on the print wheel.

United States Patent Beery v 3,712,212 Jan. 23, 1973 VARIABLE PRINTERINTENSITY CONTROL [5 6] References Cited UNITED STATES PATENTS 2,935,9355/1960 Preston et a1. ..101/93 R 3,172,353 3/1965 Helms ..101/93 C3,218,965 11/1965 Simons et a1 ..101/93 R 3,513,774 5/1970 Pawletko etal. ..10l/93 C Primary ExaminerWilliam B. Penn Att0rneyPaul W. Fish etal.

[57] ABSTRACT Apparatus for printing characters with an impact intensityvarying according to the surface area of the character being printed.Included in the apparatus is a cyclically movable character bearingmember, such as a rotary print wheel or drum or an endless belt and oneor more print hammers cooperable with the member forming a printingcouple for printing characters. An electromagnetic field produced by asolenoid initiates the flight of the hammer against a document which maybe moved relatively thereto as the printing operation is performed. Thecurrent through the solenoid coil is limited by resisters of differentvalues which are controlled by electrical gates for selectively varyingthe amount of current supplied to the coil for driving the hammer. Thetiming of the printing is kept in synchronization with the documentmovement by means of an electromechanical clock capable of divid' mgeach character position into an equal number of zones. During theoperation of the printing apparatus, the sequence of accessing thedigits to be printed, positioning the print wheel, and firing the hammercontinues as the document moves through the apparatus. Associated withthe print wheel and jointly rotatable therewith is a disk having aplurality of coded positions represented by apertures therein eachposition representing a printing character position on the print wheel.

6 Claims, 3 Drawing Figures PATENTEDJAH23 I975 SHEEI 1 OF 2 24 VDCFIG. 1. fiao 28 26 1332 I l l I l l i l iv "villi.

22 FFREG INVENTOR.

JACK BE ERY V3. i /Q ATTORNEY.

UZZQMJ PATENTEDJAN 23 I873 SHEET 2 BF 2 MEI EMESZI v wZON N mZON MZONFEE-m 50 6 :82 o ow m N GI 1 VARIABLE PRINTER INTENSITY CONTROL CROSSREFERENCE TO RELATED PATENTS AND PATENT APPLICATIONS Reference may bemade to the patent to Jack Beery U.S. Pat No. 3,573,589 entitledPOSITION SERVO SYSTEM FOR A MOTOR INCLUDING DETENT- ING AT DESTINATIONand also to the co-pending application of Richard M. Williams Ser. No.72,921, filed Sept. 1?, 1970, and entitled DOCUMENT EN- CODINGAPPARATUS.

BACKGROUND OF THE INVENTION This invention is directed to that field ofart pertaining to printing of data on record media and more particularlyto the varying of the printing impact on such media in accordance withthe surface area of the characters being printed.

SUMMARY OF THE INVENTION An important object of the invention is toprovide an improved control system for modifying the impaction of aprint hammer or the like upon record media and particularly inaccordance with the surface area of the characters to be printed.

A further important object of the invention is to provide a printer ofthe aforesaid character which includes an electronic circuit of improvedcharacter for controlling the hammer by appropriately selectedelectrical signals for varying the impact thereof upon record media.

Another important object of the invention is to provide an improvedprinter of this character which is economical to manufacture and isrugged and durable in use.

In carrying out these objects, the present invention contemplates aprinting apparatus which in its broader aspects employs electricalsignals of varying energy for modifying the operation of the printingcouple composed of a print hammer and a cyclically movable memberbetween which record media are fed. More particularly, the inventioncontemplates a control circuit associated with printing apparatus andparticularly with a document encoding station including an impact printmember cooperable with a character bearing cyclically movable member forprinting on documents moving at relatively high speeds. Included in thecontrol circuit is means which, depending upon the surface area of theselected character to be printed, can modify the current supplied by thecircuit to the energy producing means for impacting the hammer against adocument interposed between the hammer and the character bearing member.Further included in such control circuit are a plurality of electronicgates variably controlled and operated to modify the amount of currentsupplied to the hammer to vary its impact intensity.

The above'listed objects and advantages, other objects, advantages, andaspects of the invention will be more fully explained in the followingdetailed description. For a more complete understanding of theinvention, reference may be had to the following detailed description inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of apreferred circuit for varying the amount of current supplied to a printhammer driving solenoid for impacting the latter upon record media, thecircuit including an electromechanical clock generator for determiningthe firing time of the print hammer;

FIG. 2 is a chart illustrating the timing diagrams for firing the printhammer; and

FIG. 3 is a schematic view of the separate driver circuits associatedwith each hammer arid showing their connections to the hammer drivingsolenoid.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The printingapparatus to be described hereinafter may be used to encode informationon record media, such as bank checks, either in magnetic ink orconventional ink but with the characters so shaped as to be recognizedby a machine. More specifically, such printings may be in magnetic inkcharacter recognition form, referred to as MICR, or in optical characterrecognition form, referred to as OCR, depending upon the nature of theequipment for machine reading these characteristics. If desired, theprinting may be performed with magnetic ink in a font capable of beingreadily sensed by an optical recognition device. The amount of intensitywith which the print hammer impinges upon a record member or documentnot only has an effect on the appearance of the characters to the eyebut also on the machine readability thereof.

The printing couple of the illustrated embodiment of the inventioncomprises a print wheel or disk 10 rotatable about an axis 12 and havingone column of characters circularly arranged around the periphery of thewheel. One or more such sets of printing characters may be included inthe column depending upon the peripheral dimension of the wheel andother factors. Associated with the type wheel and forming the oppositemember of the couple is any suitable shaped print hammer 14. A shankmember 16, which as shown may be directly connected to the hammer, issurrounded and controlled by a coil 18 of an'electromagnetic device suchas a solenoid. In normal operation the type wheel is rotated to bring aselected character into position to be struck by the hammer 14 in theabsence of a document therebetween. In the normal operation of theprinting couple, successive documents would be fed between the hammerand the print wheel and the impact of the hammer on the document wouldcause the transfer of an ink image of the selected character onto thedocument.

The type wheel 10 may be rotated different angular distances in oppositedirections or continuously in one direction. In the former case, thewheel may be driven by a servo stepping motor which may be of thecharacter disclosed in the aforesaid U.S. Pat. No. 3,573,589, so thatthe type wheel may be stepped in opposite directions and stopped at veryfast rates. The rotatable positioning of the type wheel is accomplishedby induction coils energized by a set of coil drivers for bringing theselected type on the wheel into print position at which time the wheelis stopped to receive the impact of the hammer disposed on the oppositeside of the transport path along which the documents are fed. Asdescribed in the patent, the print wheel may be adjustably rotated ineither direction and selectively controlled to rotate the wheel in theshortest direction to bring the selected type'on the wheel into printingposition. I

Associated with the type wheel and jointly rotatable therewith on theaxis 12 thereof is a control plate or disk having a plurality of codedpositions thereon which may be a plurality of apertures through whichlight from a set of lamps generally indicated at 22 are projected andreceived by a corresponding set of photocell units each including anamplifier generally indicated at 24. Each coded position represents aprinting position on the type wheel 10. The four photocell units 24represent the binary values of 1, 2, 4 and 8 the purpose of which willbe described in more detail hereinafter.

The timing of the operation of the illustrated embodiment of theinvention is performed by an electromechanical clock including arotatable member or disk 26 rotatable about axis 28 and separate andapart from the print wheel 10 and disk 20. A circular portion of thedisk is disposed in intercepting relation between a lamp 30 and aphotocell 32. The circular portion is provided with a series of equallyspaced apart apertures (not shown) which alternately admit and interceptthe passage of light from the lamp to the photocell. Usually, the diskis rotated at a constant speed but this is not essential for theillustrated embodiment of the invention. The current generated in thephotocell as a result of the successive impingements of light therein isincreased by the amplifier 34 and then fed to a shift register 36 whichserves as a character zone counter arranged to emit pulses on channels38, 40 and 42 designated by the legends Z1, Z2 and Z4 respectively.

forming three inputs of a NAND gate 44. A fourth input to the NAND gate,that indicated at 46, bears the legend Encode. The single output of theNAND gate is connected to an inverter 48 and its output in turn isconnected to a conductor 50 along which the hammer firing signals areconducted.

As previously mentioned the intensity of the impact of the hammer isdetermined by the amount of current delivered to the solenoid coil 18.Variations in this current are provided by the series of gating circuitsillustrated in the balance of FIG. 1 and by the electrical parallelrelationship of the solenoid drivers and associated resistances ofdifferent values which are connected to a common lead extending to thecoil 18. With more specific reference to this portion of FIG. I, it isnoted that the coil is connected to a plus 24 volts do. from whichvariable amounts of current are derived for activating the coil andthereby imparting motion to the hammer 14. One lead of the coil isconnected by a common conductor 51 to two or more driver circuits whichare designated 52 and 54 and are respectively illustrated in detail inFIG. 3. The output of each driver 52 and 54 is connected to a resistance56 and 58 respectively, each of different resistive value, and these inturn are directly connected to the common lead 5] previously mentioned.Each driver circuit 52 and 54 is respectively connected to a NAND gate60 and 62. These two gates have one of their inputs connected in commonto the output 50 of the clock circuit for receiving hammer firingsignals therefrom. Each of the remaining inputs to the NAND gates 60 and62 are connected to a separate series of NAND gates, certain ones ofwhich have inputs connected to the photocell outputs PCl, PC2, lfC4 andPC8 and their respective inverted outputs PCl, W2, I 64 and W asidentified by the legends thereon.

More specifically with reference to the respective series of gatingdevices connected to the hammer driver it is noted that NAND gate 60 hasone of its inputs connected to the output of gate 64 which in turn hasone of its inputs being served by the output of NAND gate 66 and whichin turn is connected to an inverter 68 and that in turn to NAND gate 70.In this gate series, NAND gates 66 and 70 have inputs connected tocertain of the outputs or inverted outputs of the photocell units 24previously mentioned. In a similar fashion, NAND gate 62 associated withdriver circuit 54 has the second of its inputs being served by theoutput of NAND gate 72 and this gate in turn is connected to the outputof gate 74 and the latter has its input connected to the output of NANDgate 76. In this series of connected gates, it is noted that NAND gate72 and 76 have NAND gates connected to the remaining outputs andinverted outputs of the photocell units 24 previously mentioned. Inaddition, the second input of gate 64 is served by the output of gate 72and similarly the second input of gate 74 is served by the output ofgate 70 to complete the logic formulas.

The logic of these series of gates and their respective connections tothe outputs of the photocell units 24 is such that the hammer drivingcircuits are kept informed of the position of the type wheel andparticularly each printing character thereon so that regardless ofdirection of rotation of the wheel and the position at which it isstopped -to perform the printing operation the driving circuitscorresponding to the characters to be printed are either independentlyenergized or simultaneously energized to provide different currentvalues for energizing the solenoid coil 18. In other words, either oneor both of the drivers 52 and 54 can be turned on individually orsimultaneously. In this manner, three intensities of current can beobtained for the solenoid coil circuit from two driver circuits. Thefollowing chart shows the driver configurations, the driver currentbeing selected to provide the desired hammer force found necessary forgood MICR or OCR ink transfer without embossment for each characterposition on the wheel.

Medium Driver Light Driver Wheel Position waqauaunw-c l0 AMOUNT 12 ACCTNO.

13 DASH l4 OBLITERATE imum amount of current is supplied when bothdrivers are turned for printing a large surface area character such as8" is printed. All of the remaining characters may be printed using themedium current driver. The characters printed may be in fonts suitablefor MlCR or OCR characters. The energy noted in the above chart is for E13 B printing only. Such fonts differ from the conventionally shapedcharacters normally used for printing and thus their respective surfaceareas forming the image differ from their corresponding conventionallyshaped characters.

The circuits so far described will provide three different hammer impactvalues as indicated in the above chart. For more impact intensity valuesan additional driver circuit and its associated gating elements similarto those previously described and shown may be provided as indicated indotted outline at the right of FIG. 1. Such a driver circuit indicatedat 78 will be similar to the circuits 52 and 54 illustrated in FIG. 3and will include a resistance 80 which will differ in its resistivevalue from either of the two previously described resistances 56 and 58.Associated with the driver circuit 78, as previously described inconnection with driver circuits 52 and 54, is a NAND gate 82 having itsoutput connected to the driver circuit 78 and having two inputs, one ofwhich is connected to the common lead 50 from the zone counter 36 whichserves to deliver the hammer firing signals. The other input to NANDgate 82 is connected to the output of NAND gate 84 whose several inputsare connected to the photocell outputs PCl, PC2, PC4 and PC8 and theirrespective inverted outputs either directly or through one or more NANDgates in the manner previously described in connection with the gatingcircuitry for the hammer driver circuits 52 and 54. With the additionofa third driver circuit 78 and its associated resistance and gatingdevices it is possible, by judicial selection of any one or acombination of any two or all three driver circuits for energizing thesolenoid coil 18, to expand the print impact intensity capability toeight different values so that from three parallely related drivercircuits a larger number of impact intensity values are available.

The clock generator illustrated in the upper left portion of FIG. 1 isdesigned to provide eight pulses for each character position of the typewheel and thus divide each character position into eight zones. Theclock signals which are received by the zone counter 36 provide threesignals of different time durations for regulating the operation of thedifferent parts of the printing apparatus including the firing of theprint hammer. In the illustrated embodiment of the invention, theencoding is a digit-by-digit operation. The information to be encoded onthe document is withdrawn from the memory in the system and transferreddigit by digit to an encode register where it is used to position theprint wheel 10 in the manner described in the aforesaid US. Pat. No.3,573,589. The firing of the print hammer is accomplished in the last oreighth zone counted by the zone counter 36 at which time the selectedcharacter is already in position for printing and the document is movingto bring the print receiving area thereof into printing position toreceive the image of the selected character.

FIG. 2 is a timing diagram illustrating the timing of the pulsesproduced by the clock generator and by the zone counter with particularreference to the firing of the print hammer in the last counted zone.The constant frequency clock generator 26-32 produces the equally spacedapart pulses shown at 86. When the arrival of a document between theprint wheel and the hammer is sensed, such as by an appropriatelylocated photocell, a start signal is generated which is shown at 88 runsfor the period of the time that the document is in the printing station.The output 38 of the zone counter 36 represented by the legend Z1delivers a series of pulses switching or alternating between two voltagelevels each having a time duration equal to the time span between twoadjacent clock pulses as illustrated at in FlG. 2. The output 40represented by the legend Z2 delivers pulses 92 of twice the timeduration and half the frequency of the pulses 90. The third output 42represented by the legend Z4 produces pulses each having a time durationof four clock pulses as illustrated at 94 in FIG. 2. It is apparent fromthe darker area in each of the graphs represented by 90, 92 and 94 thata coincidence of a plus voltage occurs, which is an encode signal oflike sign is received on the fourth input to the NAND 44 44, willproduce, a signal such as represented at 96 on the hammer firing channel50 leading to the NAND gates 60, 62 and 82 of the circuit for energizingthe solenoid coil 18. Unless inhibited by other components in thecircuitry of the apparatus, the encode signal on input channel 46 ofNAND gate 44 continues active or high so that when Z1, Z2 and Z4 in FIG.2 are all high at one time, which is represented by time zone 7, a printsignal 96 is delivered by channel 50 to one of the inputs of each of theNAND gates 60, 62 and 82 and enabling their respective driver circuitsfor hammer activation depending upon the signals received on theremaining inputs of these gates.

The driver circuits 52 and 54 shown in FIG. 3 and the one notillustrated therein for driver circuit 78 are of conventional design andneed not be described in detail. Suffice to say that when an input pulsegoing from a value of +5 volts to ground is switched at input points, Aor B, the transistors Q1 or Q2 respectively will swing from +24 volts toless than +2.0 volts allowing the load to conduct, which load in thisinstance is the solenoid coil 18 and either or both of the resistors 56or 58. When the points A or B of the driver circuits are moved fromground to +5 volts, the transistors Q1 or Q2 turn off, and if all suchtransistors associated with the driver circuits are similarly effected,then the coil 18 is also switched off. When the coil is cut off it wantsto continue to conduct and goes to +24 volts plus an additional surgefrom the coil which may reach 400 to 500 volts. Under normal conditionssuch high voltage surges would impair if not destroy the transistorswhich may be only good for about 60 volts. To protect against suchhappenings, provision is made in the coil circuit for limiting thisinductive surge or kick" which as shown in FIGS. 1 and 3 is accomplishedby means of a diode 98 and zener diode 100 arranged as shown in FIGS. 1and 3. The diode 98 suppresses the inductive surge and the zener diodeis the controlling element allowing the voltage to go a limited distanceabove the source voltage of 24 volts but below the destructive voltageof the transistors before switching off the coil.

The operation of the embodiment of the invention illustrated herein isbelieved to be self-evident from the drawings and the above reciteddescription. First, it may be understood that one of the drivercircuits, such as 52, has a relatively high resistance 56 which rendersthis driver circuit as a low or light intensity driver, and that asecond of the driver circuits, such as 54, has a lower valued resistance58 which renders it as a medium intensity driver, and so forth for theremaining driver circuits in the system. The trains of logical gatesleading to the set of gates 60, 62 and 82 translate the characterssuccessively brought into printing position by the print wheel into thesignals which not only identify each such character but activate aselected one or selected two or more of the driver circuits forsupplying different currents for energizing the solenoid coil 18. Theelectrical parallel relationship of the driver circuits and theirrespective resistors provide a larger selection of impact intensitiesfor the different characters on the print wheel than there are driversfor propelling the single print hammer. The addition of more drivercircuits, such as represented in phantom at 78 and 80, multiplies thenumber of impact intensities available not only for printing the decimalcharacters illustrated on the print wheel 10 but also a full alphabetand additional symbols.

Although the illustrated embodiment of the invention herein employs astepping type of rotary print member capable of being reversely driven,it is to be understood that the invention is also applicable to aprinter having a character type bearing member which is continuouslymovable or rotatable in one direction. In the latter type of printingapparatus, suitable control means would be provided for signifying eachcharacter on the type bearing member as it approaches the print positionand also for controlling the energization of the solenoid coil 18proportional to the surface area of the character being printed and thuspropel the print hammer with the proper amount of energy for providinguniform printing of the characters on a record medium and while bothtype bearing member and record medium are moving. ln other words as eachcharacter on the print member moves into printing position not only isthe nature of this character recognized but also the area of its printface so that a proper amount of energy is supplied to the solenoid coilfor initiating the flight of the print hammer against the record mediumwith the desired impact so that all characters printed are all ofsubstantially the same degree of intensity.

While a particular embodiment of the invention has been shown anddescribed, it will be understood, of course, that it is not desired thatthe invention be limited thereto since modifications may be made, and itis therefore contemplated by the appended claims to cover any suchmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A printing device including, in combination;

a cyclically movable printing member carrying a plurality of printingcharacters, said characters varying to printing areas from a relativelylow to a relatively high degree,

a hammer assembly including a hammer predisposed to strike a printingcharacter brought into alignment with its path of movement and to printan image of the struck character upon a record medium interposedtherebetween and further including electrically powered means forpropelling the hammer toward the printing member,

means for moving said printing member to bring characters carriedthereby successively into alignment with the path of movement of saidhammer,

circuit means for delivering varying amounts of current to the hammerpropelling means for operating the same including a set of logic gateseach having two inputs which when concurrently signalled will activatethe gate, said gates each being capable when individually activated ofcausing the delivery of a distinctive amount of current to the hammerpropelling means for operating the same which differs from the amount ofcurrent caused to be delivered by other gates in said set of gates andalso capable when two or more of the gates of said set are concurrentlyactivated for causing the delivering of still different amounts ofcurrent to the hammer propelling means for operating the same,

means responding to the aligning of each printing character carried bysaid printing member with the path of movement of said hammer fordelivering a first electrical signal to one of the two inputs of one ormore of said logic gates, and

means also responding to the positioning of each printing character inalignment with the path of movement of said hammer for delivering anelectrical signal to the other one of the two inputs of one or more ofsaid logic gates concurrently with the delivery ofsaid first signals forselectively activating said one or more gates in accordance with thedegree of the printing area of the character brought into alignment withthe hammer with the result that the intensity with which the hammer willstrike a selected printing character can be proportioned to its printingarea.

.2. A printing device as defined in claim 1 characterized in that theelectrically powered means for propelling the hammer comprises asolenoid coil which is energized by the activation of any one or more ofsaid logic gates.

3. A printing device as defined in claim 2 characterized in that saidcircuit means further includes resistance components electricallyconnected individually to each of said logic gates which differ inresistive value from one another.

4. A printingdevice as defined in claim 3 characterized in that saidresistance components are connected in electrical series relation withtheir respective logic gates and connected to the solenoid coil inelectrical parallel relation to one another.

5. A printing device including, in combination;

a cyclically movable printing member carrying a plurality of printingcharacters, said characters varying in printing areas from a relativelysmall extent to a relatively large extent,

a hammer assembly including a hammer operable to strike anyone of theprinting characters and to print an image of the struck character upon arecord medium interposed therebetween,

means for moving said printing member to bringthe characters on themember successively into alignment with the path of movement of saidhammer,

electrically powered means for propelling the hammer against theprinting member with varying degrees of intensity including a circuithaving a plurality of resistors of different resistive values disposedin the circuit in electrical parallel relationship to one another,

control means for said hammer propelling means including switching meansindividually associated with each of said resistors and operable toeither permit or cut-off the flow of current through its associatedresistor, and

means responding to the movement of each printing character intoalignment with the hammers striking path of movement for activating anindividual one or simultaneously activating at least two of saidswitching means depending upon the extent of the printing area of thealigning character.

6. A printing device including, in combination;

a rotatable circularly shaped printing member having a plurality ofprinting characters circumferentially arranged on the periphery thereof,said characters varying in printing areas from a relatively small extentto a relatively large extent,

a hammer assembly including a hammer operable to strike anyone of theprinting characters and to print an image of the struck character upon arecord medium interposed there-between,

means for rotating said printing member to move the characters on themember successively into alignment with the striking path of movement ofsaid hammer,

electromagnetic means for propelling the hammer against the rotarymember,

means for energizing said hammer propelling means including a pluralityof logic gates each capable when separately activated of delivering adifferent amount of current to the hammer propelling means and alsocapable when two or more of the gates are concurrently activated ofdelivering still further different amounts of current to the hammerpropelling means, and

means responding to the positioning of each printing character inalignment with the path of movement of the hammer for activating anindividual one or concurrently activating at least two of said logicgates in accordance with the extent of the printing area of eachprinting character.

1. A printing device including, in combination; a cyclically movableprinting member carrying a plurality of printing characters, saidcharacters varying to printing areas from a relatively low to arelatively high degree, a hammer assembly including a hammer predisposedto strike a printing character brought into alignment with its path ofmovement and to print an image of the struck character upon a recordmedium interposed therebetween and further including electricallypowered means for propelling the hammer toward the printing member,means for moving said printing member to bring characters carriedthereby successively into alignment with the path of movement of saidhammer, circuit means for delivering varying amounts of current to thehammer propelling means for operating the same including a set of logicgates each having two inputs which when concurrently signalled willactivate the gate, said gates each being capable when individuallyactivated of causing the delivery of a distinctive amount of current tothe hammer propelling means for operating the same which differs fromthe amount of current caused to be delivered by other gates in said setof gates and also capable when two or more of the gates of said set areconcurrently activated for causing the delivering of still differentamounts of current to the hammer propelling means for operating thesame, means responding to the aligning of each printing charactercarried by said printing member with the path of movement of said hammerfor delivering a first electrical signal to one of the two inputs of oneor more of said logic gates, and means also responding to thepositioning of each printing character in alignment with the path ofmovement of said hammer for delivering an electrical signal to the otherone of the two inputs of one or more of said logic gates concurrentlywith the delivery of said first signals for selectively activating saidone or more gates in accordance with the degree of the printing area ofthe character brought into alignment with the hammer with the resultthat the intensity with which the hammer will strike a selected printingcharacter can be proportioned to its printing area.
 2. A printing deviceas defined in claim 1 characterized in that the electrically poweredmeans for propelling the hammer comprises a solenoid coil which isenergized by the activation of any one or more of said logic gates.
 3. Aprinting device as defined in claim 2 characterized in that said circuitmeans further includes resistance components electrically connectedindividually to each of said logic gates which differ in resistive valuefrom one another.
 4. A printing device as defined in claim 3characterized in that said resistance components are connected inelectrical series relation with their respective logic gates andconnected to the solenoid coil in electrical parallel relation to oneanother.
 5. A printing device including, in combination; a cyclicallymovable printing member carrying a plurality of printing characters,said characters varying in printing areas from a relatively small extentto a relatively large extent, a hammer assembly including a hammeroperable to strike anyone of the printing characters and to print animage of the struck character upon a record medium interposedtherebetween, means for moving said printing member to bring thecharacters on the member successively into alignment with the pAth ofmovement of said hammer, electrically powered means for propelling thehammer against the printing member with varying degrees of intensityincluding a circuit having a plurality of resistors of differentresistive values disposed in the circuit in electrical parallelrelationship to one another, control means for said hammer propellingmeans including switching means individually associated with each ofsaid resistors and operable to either permit or cut-off the flow ofcurrent through its associated resistor, and means responding to themovement of each printing character into alignment with the hammer''sstriking path of movement for activating an individual one orsimultaneously activating at least two of said switching means dependingupon the extent of the printing area of the aligning character.
 6. Aprinting device including, in combination; a rotatable circularly shapedprinting member having a plurality of printing characterscircumferentially arranged on the periphery thereof, said charactersvarying in printing areas from a relatively small extent to a relativelylarge extent, a hammer assembly including a hammer operable to strikeanyone of the printing characters and to print an image of the struckcharacter upon a record medium interposed therebetween, means forrotating said printing member to move the characters on the membersuccessively into alignment with the striking path of movement of saidhammer, electromagnetic means for propelling the hammer against therotary member, means for energizing said hammer propelling meansincluding a plurality of logic gates each capable when separatelyactivated of delivering a different amount of current to the hammerpropelling means and also capable when two or more of the gates areconcurrently activated of delivering still further different amounts ofcurrent to the hammer propelling means, and means responding to thepositioning of each printing character in alignment with the path ofmovement of the hammer for activating an individual one or concurrentlyactivating at least two of said logic gates in accordance with theextent of the printing area of each printing character.